1. Field of the Invention
The present invention relates to a differential low-noise amplifier that differs from prior art differential low-noise amplifiers in that it includes series resonance and parallel resonance resonators to render it frequency selective.
2. Description of the Prior Art
One prior art differential low-noise amplifier is described in published European patent application EP 1 548 932, for example.
For a differential low-noise amplifier of that kind to be used in a radio signal receiver circuit, it is generally necessary to place it between two filters, an anti-blocking filter being disposed between a receiver antenna and the amplifier itself and an image rejection filter being disposed at the output of the amplifier.
The anti-blocking filter is necessary to prevent the receiver circuit from becoming saturated in the presence of strong out of band interference signals known as blocking signals. The image rejection filter is necessary to reject signals in the image band in the case of a “heterodyne” receiver.
It is also necessary to verify the matching of impedances between the antenna, the filters and the amplifier. The input impedance of the amplifier must correspond to the output impedance of the anti-blocking filter. Similarly, the input impedance of the anti-blocking filter must correspond to the impedance of the antenna and the output impedance of the amplifier must correspond to the input impedance of the image rejection filter.
Thus a radio signal receiver circuit includes a plurality of elements (amplifier, filters) whose input and output impedances must be matched.
The invention aims to solve the problems linked to the complexity of existing receiver circuits by providing a selective differential low-noise amplifier that does not necessitate the addition of antiblocking or image rejection filters on the upstream or downstream side or of impedance matching circuits.